It can be assumed that the brain is optimally designed for the processing of "real- world" sensory information, so that we can react in appropriate manner when confronted with environmental stimuli. Despite this fact, a large portion of mental life consists not of the processing of actual information, but rather the rehearsal of what to do when we encounter stimuli from the environment (Klinger, 1978). This rehearsal and the cognitive skills involved are likely to have a strong adaptive value.
Present neuroimaging data suggests that this "non-real" information, or information not tied to any current environmental stimuli, is treated in a similar fashion as information processed in a real physical environment. Data from a neuroimaging study, specifically using positron emission topography (PET), supports the notion that when we imagine something of a visual nature and manipulate that image, our visual cortex is activated (Kastner et al., 1999). Likewise, in studies that control for actual movement, it has been shown that by simply imagining the actions involved in a repetitive motor task, the physical representation of the associated pattern of activity in the motor cortex increases (Pascual-Leone et al., 1995).
A question, then, is why would mental imagery of a physical activity activate the same brain regions as the activity itself? This double-activation would make sense if mental imagery reflects exercise/practice for the brain (or if imagining a thing and "really" doing a thing are not as distinct as many assume they are). By being able to practice a response, or exercise a part of the brain without having to physically experience a behavior-eliciting stimulus (especially one that is potentially dangerous), we can optimize mental functioning and, ultimately, our response to an actual situation (Cumming and Hall, 2003). It is well known that mental imagery techniques greatly facilitate multiple aspects of performance from sports to music (e.g., Feltz and Landers, 1983). Further, the most successful individuals at creative endeavors are usually those that have the best imagery skills (Intons-Peterson, 1993). Thus, it appears advantageous to be able to create vivid representations in the mind's eye of various scenarios, which in fact, is what dreaming entails.
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